A major emphasis of this program of research has been to define the relationship of exogenous hormones to subsequent cancer risk. An analysis within the context of a large screening program showed an excess risk of breast cancer associated with menopausal hormone use, with combined estrogen-progestin regimens increasing risk beyond that associated with estrogens alone. Hormone effects appeared to predominate among thin women, suggesting that endogenous hormones among heavier women may outweigh the effects of supplemental hormones. Additional analyses are ongoing to clarify relationships for subgroups of tumors (such as those defined by hormone receptor status) as well as to assess relationships of hormone use with other cancers (including endometrial, ovarian and lung cancers). Effects of oral contraceptives on cancer risk have also been pursued in several investigations. In a study of cervical adenocarcinomas, use of oral contraceptives appeared to increase the risk of in situ tumors. Also underway is a retrospective cohort study to evaluate cancer risk following different types of infertility and exposure to ovulation- stimulating drugs. In a comparison study in Denmark, cancer risks among children conceived following use of these drugs is being pursued. Also of interest is the relationship of breast implants to subsequent cancer risk. Breast cancer risk has been of concern, given that breast implants can interfere with the mammographic visualization of lesions. However, in a large retrospective study that we conducted, we found no evidence for an alteration in breast cancer risk. Currently underway are analyses of risk of other cancers, connective tissue diseases and mortality related to breast implants. A study of women who experienced breast reduction operations, conducted to assess reasons for a well demonstrated reduction in subsequent breast cancer risk, has shown that risk is inversely related to the amount of breast tissue removed. Finally, efforts are being made to assess risk of several cancers in relation to different types of gynecologic operations. Of interest are not only operations involving ovarian ablation but also those with more subtle effects, such as tubal ligation. Although this procedure has been linked with substantial decreases in the risk of ovarian cancers, its effects on other tumors (e.g., breast) are less well known. Analyses within the context of two case-control studies showed no alteration in risk of either breast or endometrial cancers associated with tubal ligations.